1. Field of the Invention
This invention relates to a process for deoiling and dewatering refinery sludges in which sludges optionally mixed with a diluent oil, such as recycle oil recovered in the process, are contacted with steam or superheated steam in a heating zone to effect separation of the sludges into dry, free-flowing solids having a substantially reduced oil content, and an oil-water vapor phase. Condensation of the oil-water vapor phase withdrawn from the heating zone yields an oil phase and a water phase which can be conveniently separated to yield oil suitable, for example, as a cracking feedstock and water with a reduced Chemical Oxygen Demand.
2. Description of the Prior Art
Petroleum based refinery sludges are widely encountered waste by-products of the petroleum refining industry. Such sludges are typically stable emulsions of oil, water and solid particulates. The solids originate as sands and clays contained in crude oil, stray catalyst particles, coke fines and as precipitates, scale and rust derived from various refinery processes, etc.
Since petroleum sludges are produced continuously in refineries, they pose a constant disposal problem. For example, large amounts of sludges accumulate on the bottoms of settling ponds used to remove suspended matter from refinery water effluent streams. Eventually, the pond bottoms must be dredged in order to maintain effluent quality and large volumes of sludges are generated for disposal. API separator bottoms and oilsoaked sand and soil resulting from oil spills also contribute to the sludge disposal problems of refineries. The nature of the sludge compositions has made it difficult over the years to economically deoil and dewater the sludges for pollution-free disposal.
Incineration offers one means of disposing of these sludges. However, the complex nature of such materials make it necessary to provide substantial air pollution control facilities to prevent atmospheric pollution during burning operations. Also, only a fraction of the value of the oil content in the sludges can be recovered in the form of heat and some method of disposal is still required for the non-combustible solids which form an appreciable part of the sludges.
Various processes have been advanced for deoiling refinery sludges to recover the oil contained therein for re-use. However, such processes have not been adopted to any great extent by the industry. For example, the use of both benzene and naphtha with added water in attempts to deoil sludges has been found economically unattractive because the pond settling characteristics of the resulting mass is generally unsatisfactory. Likewise, attempts to deoil and break sludges with iso-octane and gas oil have not been generally successful because the oil phase and the water-solids phase do not separate.
A typical petroleum sludge contains about 35% solids, about 38% water, with the balance being oil. The high content of the oil and its value as a cracking stock make it desirable to recover as much of the oil present in the sludges as possible for removal and recycling to the refinery cracking unit. There is a need in the art, therefore, for the economic process to recover this oil while at the same time producing a readily disposable solid and desirably one in which the water content of the sludges issuing from the process has a reduced Chemical Oxygen Demand.
One of the principal objects of this invention is to provide a process for recovering dry, free-flowing solids having a substantially reduced oil content from refinery sludges.
Another object of this invention is to provide a continuous process by which refinery sludges can be deoiled and dewatered under substantially atmospheric pressure conditions.